The power generating element forming this battery is what is called a winding-type battery element and is especially a power generating element formed into a flat shape in order to respond to requests for a thin power generating element.
Such a power generating element is basically formed by winding a foil-shaped positive electrode plate and the foil-shaped negative electrode plate, on which active material layers are formed respectively, about a winding core, with separators sandwiched therebetween and is formed into the flat shape by forming the winding core itself into a flat shape as described in below-described Patent Document 1, for example, or by winding the foil-shaped positive electrode plate and the like about a circular cylindrical winding core and pressing and flattening them.
By forming the power generating element into the flat shape to thereby obtain the thin power generating element as described above, it is possible to achieve satisfactory radiation performance. Moreover, when the battery case in a shape of a rectangular parallelepiped is used, the flat power generating element has an advantage that a dead space between the power generating element and an inner face of a case is small, and therefore the power generating element can be disposed while effectively utilizing a capacity in the case.